Researchers remain hopeful that they're heading in the right direction to finding a cure for HIV, the virus that causes AIDS. Right now, it’s still out of reach. But the unusual cases of three people may hold clues.

Perhaps the best known is the “Berlin patient,” Timothy Ray Brown. He’s the first and only person ever to be cured of HIV. Brown found out in 2006 that he had acute myeloid leukemia. He already knew he had HIV and had been taking medicine for it for years.

After chemotherapy didn’t help his leukemia, Brown went to Berlin, where he got two bone marrow transplants from an HIV-resistant donor. Ten years later, Brown is leukemia- and HIV-free. Other HIV-positive leukemia patients who got similar treatments haven’t been free of HIV. Experts still don’t know why Brown became free of HIV.

Clues From Babies

Usually, infants who are born to HIV-positive mothers get medications to prevent the becoming infected themselves. Only after two tests come back showing HIV infection do doctors switch to drugs that treat HIV. The first test isn't recommended until the baby is 2-3 weeks old.

Sometimes doctors take a different approach. A baby from California born to a mother with AIDS got the treatment medicines, called antiretroviral therapy (ART), when she was only 4 hours old. At 9 months, back in 2014, she was still HIV-negative -- and was still getting ART.

Another case also made headlines. Doctors gave a baby from Mississippi treatment medications just 30 hours after she was born to a woman who had HIV. The little girl tested HIV-free for more than 2 years, and some people said she was “in remission” at the time, which was in 2013.

But in 2014, at age 4, HIV turned up in the Mississippi baby’s blood. Her mother had stopped giving her ART when she was 18 months old, against medical advice.

The “Mississippi baby, "whose name hasn’t been made public, went back on ART. She finished kindergarten in June 2016 and is “doing great,” Hannah Gay, MD, who treated the baby at the University of Mississippi Medical Center, says in a news release.

Gay says she’s making a scrapbook for the little girl so she can one day know more about the role she played in helping experts better understand HIV.

HIV Hides in the Body

Scientists had hoped giving strong treatment medications so soon after birth would get rid of the virus or prevent it from spreading and doing damage.

The fact that the HIV virus eventually turned up in the “Mississippi baby” isn't unexpected, says Robert Siliciano, MD, PhD, professor of medicine in the infectious diseases department at Johns Hopkins University School of Medicine. It supports the theory that HIV cells stay in the body, just out of view in a hidden "reservoir."

"Curing HIV infection is going to require strategies to eliminate this reservoir," he says.

Start Treatment Earlier

People who have HIV should start treatment as soon as they know. That's easier to do for babies, who can be tested and retested right after they're born. Adults rarely know exactly when they're infected.

If you're at risk, getting tested for HIV more often may lead to earlier, more effective treatment. Studies have found that those who adhere to their treatment and maintain a healthy lifestyle can not only live longer, but have virtually the same life expectancy as someone who is not infected.

When someone tests positive in a clinic, for example, it might make sense for a doctor there to "start treatment and ask questions later," says David Hardy, MD, a board member of the HIV Medicine Association. Still, patients will need to understand their diagnosis and the treatment and be willing to commit to what is currently a life-long treatment.

And until there are better tests to find the virus hiding in the body, doctors can't accurately call anyone "HIV-free."